The invention relates to a gear unit for a delivery pump installed in a deep borehole and having the characteristic features described in the preamble of Claim 1.
Rotating deep-borehole pumps, especially those for the delivery of petroleum, are arranged at the foot of the borehole. They are driven by a rotating rod, which extends beyond the borehole, via a gear unit driven by an electric motor. The drive rod has a small diameter in comparison with its length. When a torque is applied to drive the deep-borehole pump, the drive rod twists in its elastic region and thus acts as a torsion spring which, due to its length, is capable of storing a lot of energy. When the electric motor is switched off or electric power is interrupted, the stored energy is released and introduced into the gear unit and electric motor via the output shaft of the gear unit. Since the running resistances of the gear unit and electric motor are quite low, and the gear unit further increases the RPMs as a function of its gear ratio, extremely high speeds can result from the stored energy when the motion is reversed, which speeds are capable of destroying the entire drive unit in an explosive manner. The drive unit must therefore be equipped with a braking device which makes possible the controlled reduction of the stored energy. Mechanical braking systems have the disadvantage that they are difficult to modulate, are subject to considerable wear, and the pump shaft remains under initial stress (risk of accident).
WO 97/10437 makes known a drive unit for a deep-borehole pump in which a fluid pump is used for the controlled reduction of stored energy from the gear unit output shaft. The fluid pump is connected through a freewheel clutch with a shaft of the gear unit. During normal operation, i.e. in the direction of delivery of the deep-borehole pump, no rotational motion is transmitted from the freewheel. When the direction of rotation is reversed, the rotational motion is introduced into the fluid pump. In the process, the fluid pump draws in a viscous fluid from a reservoir and returns it via a restrictor. The restrictor is adjusted or dimensioned such that during the reverse rotation, a gradual reduction of the stored energy occurs and the drive unit thus remains within the allowable RPM-range.
The object of the invention is to design the generic gear unit such that the input shaft is arranged horizontally and the stored energy from the drive shaft can be dissipated in a simple and controlled manner.
In a generic gear unit, this object is achieved according to the invention by the characteristic features of Claim 1. An advantageous embodiment of the invention is the subject of the subclaim.
The invention has a gear pump integrated into the gear unit, the pump acting as a return-motion brake. Based on the use of a right-angle unit, the input shaft can be arranged horizontally with the drive shaft being vertical as required. The result is a compact gear unit for driving the deep-borehole pump.
The invention is based on the principle that in a gear pump, as is well known, the direction of delivery of fluids is a function of the direction of rotation. In the invention, this fact is exploited through the arrangement of the gear pump such that in the gear unit""s direction of operation, air is drawn in at the inlet side, with the result that no fluid is conveyed. In the direction of rotation, which occurs when the gear unit is driven by the stored energy from the drive shaft of the gear unit and the drive rodding of the deep-borehole pump, fluid is conveyed and pressure is built up since the inlet side is located below the level of the fluid. The fluid used is oil which serves simultaneously as a lubricant for the gear unit. The oil is sent into a pressure chamber. The pressure chamber is connected through a restrictor to the interior of the gear unit. The restrictor causes an increase in pressure and thus a controlled reduction in the stored energy. As the RPMs increase, the torque of the gear pump rises and is used for braking.
An embodiment of the invention is shown in the drawing and is described in more detail below: